Investigation of Faceted Crack Initiation and Propagation in Near-alpha Titanium Alloys
It is widely recognized that titanium alloys can fail by internal crack initiation at room temperature when loaded under fatigue and creep conditions. Frequently, initiation sites show evidence of extensive faceting that has been associated with marked decrease in life, especially when induced by the application of a sustained load hold at peak stress. Despite the prevalence of faceted cracking,the mechanisms by which cracks nucleate and propagate have not been thoroughly investigated. In this work, we apply an array of microscopy techniques to the examination of initiation and propagation facets on the primary fracture surface of a titanium alloy that failed under dwell loading conditions. Quantitative fractogra-phy and EBSD revealed the gross spatial and crystallographic orientations of the facet planes,site-specific thin foil extraction techniques coupled with transmission electron microscopy (TEM) experiments have allowed for the characterization of deformation structures beneath facets at two dwell fatigue crack initiation sites. The experimental observations demonstrate that the crack initiation sites each contained a glassy facet with a very near-basal orientation that was substantially inclined to the loading direction surrounded by rougher facets oriented nearly orthogonal to the loading direction. TEM analysis of the latter facets revealed extensive basal slip,yet crack propagation occurred on irrational hkil planes that were inclined to (0001) and not along slip bands as previously suggested. The dislocation activities beneath the facets clearly demonstrate that planar slip and extended pile-up structures at grain boundaries play a prominent role in faceted crack initiation and growth.
Dwell fatigue crack initiation facets crack growth EBSD fractography
Adam L. Pilchak Matt C. Brandes Robert E. A. Williams James C. Williams
Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXLM, Wright Patterson The Ohio State University,Department of Materials Science and Engineering, Columbus,OH 43210 USA
国际会议
The 12th World Conference Titanium(第十二届世界钛会 Ti-2011)
北京
英文
993-997
2011-06-19（万方平台首次上网日期，不代表论文的发表时间）